Case hardening



Patented Apr. 10, 1934 John J. Egan, Brooklyn,

Metallurgical Compa y,

Virginia No Drawing. Application August 11, 1931,

the surface- In this process the surres PATENT OFFICE CASE HABDENING Serial No.

N. Y., assignor to Elect! a corporation of West 3 Claims. (01. 14 8--17) My invention relates to the production of hard wear-resistant cases or surface layers the carbonizing process,

improved method of proon ferrous referring enriched cases on carbonizing face portions of low-carbon steel are enriched 1 with carbon by the action at elevated temperatures of various carbonaceous materials. In

order to secure proper penetration of carbo the materials must be maintained at an elevated temperature for a number of hours,'which in- A method which volves considerable expense.

would reduce the time required to produce a case of given depth would result in savings not only in the cost of heating, but also in apparatus involved.

the cost of It is the object of my invention to accelerate and intensify the action of gaseous carbonizing agents on ferrous materials, so as toreduce materially the time required to produce a case of given hardness or depth. This object I have attained by the application of my discovery that electrical influences which tend to ionize the gaseous environment of the articles being treated s0 accelerate and intensify the carbonizing reaction that cases of given de may be produced time. The ionizing pth and hardness in much less than the usual influence may be generated by an arc, spark, corona, or o trical discharge in the gaseous ther form of elecenvironment.

the preferred form of my inventreated are placed in a aseous carbonizing agent or agents, and an electrical discharge is caused to take place within the chamber, preferably article. ture is maintained in close proximity to the surface of the The customary carbonizing temperaand the discharge is continued throughout the entire time of heating.

Suitable electrodes across may be drawn can easily chamber. ordinary internal combustion is an especially convenient form this purpose. With one or more spark plugs disonment of the able to produce on typical from two to six times charging within article I have been o vcarbonizing steels cases the gaseous envir engine which the discharge be inserted into the A spark such as that generated at an spark plug of discharge for as deep as those produced in the same time and at the same temperature ionizing influence. The improvement the use of my method depends in the absence of the secured by somewhat on the and the carbonlzing agent used.

but my invention gives beneficial effects of appreciable magnitude on any carbonizlng steel or with any gaseous carbonizing agent. Tests which Lhave made demonstr ate clearly the acceleration which results from the use of my invention. For example, a cold rolled low-carbon steel treated for 2 hours with illuminating gas at 915 C. formed a carbonized case 0.02 inches deep when a spark was used in the treating chamber, while without the spark a treatment for 2 hours at 915 C. in illuminating gas formed a case only 0.005 inches deep, as was to be expected from general experience in the art. Using the same steel and treating for 2 hours at 915 C. in an atmosphere of propane, the corresponding depths of cases were found to be 0.06 inches in the presence of a spark within the chamber and only 0.01 inches in the absence of an ionizing influence.

Further tests which I have made show that the principle of my invention may be applied with beneficial results on any carbonizing steel and in any carbonizing atmosphere, and with the use of any of the usual carbonizing temperatures. Therefore I do not wish to be limited to or by the specific examples which I have disclosed herein, or to the preferred form of my invention I wish to be limited only by the prior art and the appended claims.

I claim: a

1. The method of carbonizing ferrous articles which comprises heating the articles in a chamber containing a carbonizing gas while maintaining an ionizing electrical discharge in close proximity to the surface of said articles, the discharge providing no material portion of the heat required to maintain the articles at carbonizing temperatures.

2. The method of producing carbon-enriched surface portions on at least part of a low-carbon ferrous article which comprises heating the article in a chamber containing propane; while maintaining in close proximity to the surface of said article an ionizing electrical discharge, which provides no material portion of the heat required to maintain the articles at carbonizing temperatures.

' 3. The method of producing carbon-enriched surface portions on at least part of a ferrous article which comprises heating said portions in the presence of a carbonizing gas while maintaining in close proximity to the heated portions at least one of the following ionizing electrical discharges: are, spark, corona, the discharge providing no material portion of the heat required to maintain the articles at carbonizing tempera- 

